Speed and load regulating device for hydraulic transmissions



Oct. 27, 1936. H. w. LINK 2,058,394

SPEED AND LOAD REGULATING DEVICE FOR HYDRAULIC TRANSMISSIONS Filed Oct. 5, 1952 m '40 I s Harry W Li 72K WZQMVW A. iiowflc y Patented Oct. 27, 1936 SPEED AND LOAD BEGULATING DEVICE FOR HYDRAULIC TRANSMISSXONS Barry w. Link, Philadelphia, rgminm. by mesne assignments. to American Engineering Company, Philadelphia, Pa... a corporation of Pennsylvania Application October 5, 1832, Serial No. 636,321

l Ciaims. (Cl. 80-53) This invention relates to speed and load regulating devices for hydraulic transmissions. In

transmissions of the type employing pump and motor units it has been found that as'the load increases the speed thereof decreases due to the increasing leakage of fluid in both the pump and motor of said transmission. This change in speed of the transmission for each change in load is extremely undesirable especially where constant speed transmissions are required, and it is the principal object of the present invention to provide means for compensating for this leakage to insure a constant running speed of the transmission for all loads. V A further object of the invention is to provide means for bypassing the fluid discharging from the pump to the motor of the transmission when the load reaches a predetermined maximum thereby interrupting the operation of the motor, and to cause renewal of operation of said motor when the load decreases from this predetermined value.

Other and further objects will become apparent as the description of the invention progresses.

Of the drawing:

r Fig. 1 is a general plan view showing an hydraulic transmission and a speed and load regulating device associated therewith.

Fig. 2 is a sectional view taken through the speed and lead regulating device comprising the present invention.

Referring to the drawing, the numeral i indicates an hydraulic transmission comprising a pump 2, and an hydraulic motor 3, of the general type disclosed. in United States Patent No. 1,077,979. Pump 2 is driven at a constant rate of speed by an electric motor 4 and the fluid delivered by said pump to motor 3 flows in the direction of the arrows through pipe connections 5 and 6 causing rotation of the motor 3 in a well known manner. The hydraulic transmission l and electric motor 4 are suitably supported upon a reservoir casing I. Fluid may be drawn into the transmission i from this reservoir for makeup purposes through pipe 9.

The leakage occurring in transmissions of the character set forth has been found by experimentation to vary from zero at no load to a maximum of substantially six percent of the fluid pumped at full load conditions. Due to this leakage, the speed of rotation of motor 3 falls oil as the load increases.

I have devised a speed and load regulating device i0 which compensates for the leakage oo- 55 curringin the transmission, and thus insures con- 28 extends.

stant speed of the motor 3-for all loads. This device is so adjusted that'when the transmission I is operating under no load conditions, substantially six percent of the fluid delivered to motor 3 by pump 2 is bypassed. The amount of fluid bypassed through this regulating device l0 decreases as the load imposed upon the transmission increases, and when full load conditions are attained and the leakage in the transmission reaches a maximum, no fluid is bypassed through the regulating device. By this device, it is seen that the motor 3 will operate at a constant speed for all loads. Referring'to Fig. 2, the regulating device It, comprises a substantially cylindrical casing ll having provided therein chambers I2, I! and I4 separated by partitions i5 and i6. Partitions I! and i6 and the bottom wall I! of casing ii are provided with aligned apertures which removement. The lower end of valve I 8 extends through and is guided in an aperture provided in the end wall I! of a cylinder 20 secured to the lower end of easing I l by any suitable means. A piston 2i operating in cylinder 20 is secured to valve il near the lower end thereof. A cap 22 is secured to the upper end of easing ii and has provided therein a tapped aperture 23 into which a plug 24 is adiustably secured. Plug 24 is provided'with an aperture 25 through which a rod The lower threaded end 21 of rod 28 extends through atapped aperture 28 provided in a disk 23 resting upon an annular shoulder 3| provided at the upper end of casing II. A nut Si is secured to the upper threaded end 33 of valve II and a disk 32 slidably mounted on ceive and guide, a valve member-l8 for axial said valve is positioned therebeneath. Rod 26 rests upon upper end of valve i8 and a purpose thereof, as will hereinafter appear, is to ailord a means for adjusting the initial position of said valve. A coil spring 34 encircles the upper end of valve II and extends between disk and the bottom wall of chamber i2. A second coil spring II encircles rod 26 and extends between disk 29 and a disk 36 positioned adjacent plug 24. The tension of springs 34 and 35 may be adjusted by simply adjusting nut 3i and plug 24, respectively. Valve II is provided with a reduced portion 31 intermediate the ends thereof which is adapted to extend through the aperature-provided in partition l8 and thus establish communication between chambers l3 and I4. Valve I8 is also provided with a series of graduated grooves 38 extending upwardly from the reduced portion 31 thereof. These grooves are so constructed and arranged that when valve i8 is in its lowermost position, the solid portion thereof completely seals the opening between chambers I3 and I4. However, as valve I8 moves upwardly, due to the construction of grooves 38, progressively larger quantities of fluid may pass from chamber I3 to chamber I4, and when the upper shoulder of reduced portion 31 rises above the bottom wall of chamber I3 substantially free flow of fluid between said chambers is established. A pipe 39 connects chamber I3 with pipe 5, and a second pipe 48 connects chamber I4 with the reservoir 1 so that fluid discharging from pump 2 may circulate through pipe 39, chamber I3, chamber I4, and pipe 40 to the reservoir when communication is established between chambers I3 and- I4 by adjustment of valve I8. A branch pipe 4i connects the upper end of cylinder 20 with pipe 39, thus the pressure of the fluid in the system is communicated to piston 2I which adjusts valve I8 accordingly. Pipes 42 and 43 extending from the lower ends of chamber I2 and cylinder 20, respectively, are connected to a drain pipe 44 which communicates with reservoir I, thus any fluid leaking past valve I8 or piston 2I will drain to the reservoir];

The transmission I is shown geared to a machine 45 which may be of any type requiring constant speed of operation. The machine 45 may, for example, be a machine employed to test the tensile or compressive strength of such materials as steel, wood, or concrete.

The mechanism just described operates briefly as follows. When no load is imposed upon the transmission I practically no leakage takes place therein. Accordingly, valve I8 is adjusted longitudinally by turning rod 26 until the grooves-38 provided thereinpermit substantially six percent of the oil discharging from pump 2 to motor 3 to bypass from chamber I3 to chamber I4, and thence to the reservoir 1, thus depriving motor 3 of substantially six percent of the oil discharging from pump 2.

It will be remembered that when the transmission is operating under full load conditions substantially six percent of the-fluid discharging from pump 2 is lost by leakage in the transmission. Thus by adjusting valve I8 so that at no load conditions the motor .3 will also be deprived of six percent of the fluidflowing through thesystem, the speed at which motor 3-is operated at no load conditions will be the same as that at which it operates at full load conditions. 'As the pressure in system builds up piston 2| will move valve I8 downwardly against the tension of spring 34. When this occurs the grooves 38 provided in valve I8 will be partially covered thus permitting a smaller quantity of fluid to flow from chamber I3 to chamber I4. The difference in the amount of fluid bypassing from 'chamber I3 to chamber I4 for this particular-pressure,- and that bypassing therebetween for -'no load conditions, corresponds substantially with the amount of leakage occurring in the' transmission. Thus the motor 3 will still be operatedat' a constant speed. A

When the transmission is operating under full load conditions valve I8 will be lowered to such an extent that the opening between chambers I3 and I4 is completely closed; thus no fluid can bypass between said chambers. Under full load conditions the leakage of the transmission is substantially six percent of the total fluid discharged and constant speed of rotation of motor 3 is there'- fore maintained. When the load imposed upon the transmission decreases spring 34 will urge valve I8 upwardly in accordance with the drop in pressure, thereby permitting an amount of fluid to bypass from chamber I3 to chamber- I4 equivalent to the difference in amount of leakage in the transmission. It therefore is seen that motor 3 will operate at a constant speed regardless of the load imposed upon the transmission.

It sometimes is desirable, in certain types of machines, that a constant load be maintained. For example, in testing machines it may be desired to impose a certain constant load upon the :object to be tested, and to note the elongation thereof at different intervals of time. In ordc. to maintain a constant load on the object to be tested, the rotation of motor 3 must cease when the predetermined load is attained to prevent increasing the load, and a suitable brake mechanism must necessarily be employed in the testing machine to prevent reversal thereof which obviously would cause a rapid reduction in the load. To prevent further operation of motor 3 after the predetermined load has been obtained, the following mechanism is provided.

' Referring to Fig. 1, it will be observed that the machine 45 has attached thereto a pressure gauge 48. This gauge is so constructed that when the pointer 41 thereon registers a predetermined pressure, electrical contacts thereon will close the circuit leading thereto from a suitable source of electric power 60. This type of gauge is well known and a detailed description thereof is unnecessary. For a complete disclosure of such a gauge reference may be had to United States Patent No. 878,423, granted February 4, 1908. A pair of conductors 48 and 49 lead from the contact points of gauge 46 to a switch 50. A second pair of conductors 5| and 52 lead from switch 50 to the coil of a solenoid 53, the armature 54 of which being connected to the lower end of valve I8 of the regulating device In by a coupling 55. It therefore is seen that when gauge 45 registers the predetermined load imposed upon machine 45 by transmission I, the circuit will be closed, causing energization of solenoid 53 with the result that valve I8 will be operated to its uppermost position. When valve I8 assumes this position, fluid will freely bypass from chamber I3 to chamber I4 and substantially the total amount of fluid discharging from pump 2 will flow through pipe 38, chamber I3, chamber I4, and pipe 40 to the reservoir 1, and consequently motor 3 will come to rest.

When the load falls oil! due, for example, to

elongation of the object tested, the circuit will be interrupted and solenoid 53 will be deenergized. When this occurs spring 35 will urge valve I8 downwardly and the pressure in the system will build up causing piston 2| to urge valve I8 downwardly, causing the latter to compensate for the leakage in the transmission. Motor 3 will now actuate machine 45 to reestablish the load, and when the predetermined load has again been established electrical contact will again be made in gauge 46 and solenoid .53 will again actuate valve I8 to its uppermost position causing the fluid discharging from pump to flow to the reservoir 1 through the connections previously described, and thus interrupt operation of motor 3.

It therefore is seen that I have provided an effective regulatingdevice which maintains a constant speed of operation of an hydraulic transmission. The device may also be utilized to maintain a constant load upon a machine driven by said transmission.

The regulating device herein described has, for

the purpose of illustration, been shown as apv plied to an hydraulic transmission. It is obvito-limit the invention to the single embodimentherein shown since it may be embodied in other forms, all coming within the scope of the claims which follow.

What is claimed is:

1. In a device of the class described, the combination with a transmission including a pump and a motor, of adjustable valve means for compensating for the leakage in said transmission to maintain constant the speed oif operation ofsaid motor,

fluid pressure means for adjusting said valve means, and additional means for adjusting said valve means to fully open position to bypass the total discharge of said pump to exhaust.

2. In a device of the class described, the combination with an hydraulic transmission including a pump and a motor, of adjustable valve means for compensating for the leakage in said transmission to maintain constant the speed of operation of said motor, fluid pressure means for adjusting said valve means, and a solenoid for actuating said valve means to fully open position to bypass the total discharge of said pump to exhaust.

3. In a device of the class described, the com bination 01 a transmission including a pump and a motor, pressure and suction connections between said pump and motor, means for compensating for leakage in said transmission to maintain constant the speed of operation of said motor, said means comprising an adjustable valve operameans for adjusting said valve in accordance with the load imposed upon said motor, to permit progressively smaller quantities of the fluid discharged by said pump to bypass to exhaust as the load imposed upon said motor increases, and additional means for adjusting said valve to fully open position to bypass the total discharge of said pump to exhaust.

4. In a device of the class described, the combination of a transmission including a pump and a motor, pressure and suction connections between said pump and motor, means for compensating for leakage in said transmission to maintain; constant the speed oi operation of said motor, said means comprising an adjustable valve operatively connected to said pressure connection,

means for adjusting said valve in accordance with the load imposed upon said motor, to permit progressively smaller quantities of the fluid discharged by said pump to bypass to exhaust as the load imposed upon said motor increases, and a solenoid for-adjusting said valve to fullyopen position to bypass the total discharge of said pump to exhaust.

RY W. LINK.

"tively connected to said pressure connectlom 

